Rectangular to ridged waveguide transition having separate mode converting and impedance matching sections



Nov. 17, 1964 R. M. WHITE 3,157,845

RECTANGULAR TO RIDGED WAVEGUIDE TRANSITION HAVING SEPARATE MODE CONVERTING AND IMPEDANCE MATCHING SECTIONS Filed Jan. 29. 1965 3 Sheets-Sheet l INVENTOR RICHARD M. WHITE ATTORNEY 3,157,845 ON HAVING ANCE Nov. 17, 1964 WHITE AVEGUIDE TRANSIT VERTING AND IMPED NG SECTIONS RECTANGULAR T0 RIDGED W SEPARATE MODE CON MATCHI Filed Jan. 29, 1963 5 Sheets-Sheet 2 x i x w N,////

INVENTOR.

RICHARD M. WHITE ATTORNEY Nov. 17, 1964 R. M. WHITE 3,157,845

' RECTANGULAR TO RIDGED WAVEGUIDE TRANSITION HAVING SEPARATE MODE CONVERTING AND IMPEDANCE MATCHING SECTIONS Filed Jan. 29, 1963 3 Sheets-Sheet 3 J1 fC X ra Fig.4]

INVENTOR. RICHARD M. WHITE ATTORNEY United States Patent 3,157,845 RECTANGUEJAR Tl) REBGED WAVEGUTE TRAN- SETION HAVlNG SEPARATE MODE CQNVERT- ING AND IMPEDANCE MATCHHNG SEQTTGNS Richard M. White, Berkeley, Calif assignor to General Electric Company, a corporation of New York Filed .lan. 2%, 1363, Ser. No. 254,793 7 Claims. (6i. 333--21) This invention relates to waveguide transmission devices and more particularly to transitions for transferring microwave energy between a rectangular waveguide and a ridged waveguide.

It is often useful to employ different microwave waveguides in the same system for transmitting microwave energy. The employment of different waveguides makes most effective use of the respective mechanical and electrical properties of the waveguides. For example, it is often desirable to use both rectangular and ridged waveguides, because ridged Waveguide, although more expensive and difficult to manufacture than rectangular waveguide, is characterized by certain advantages over rectangular waveguide including a broader bandwith, a longer cut-off wavelength for a given waveguide size, and a lower characteristic impedance.

In such a system it is necessary to provide transitions for transferring microwaves from rectangular waveguides to ridged waveguides, from ridged waveguides to rectangular waveguides, or in both directions between rectangular and ridged waveguides. To make best use of the capabilities of both types of waveguides, the transition should provide for the lossless transfer of microwaves over a broad frequency range and should effect such transfer without substantial reflection of the microwaves incident on the transition. Additionally, it is desirable for the transition to be compact, easily and accurately designed, and readily machined. The structure of such a transition is complicated by the necessities of providing a smooth transformation of impedance between the two types of Waveguides to be coupled and of providing for the reorientation of the field configurations in the two waveguides. The transitions heretofore available, however, have usually been subject to a number of disadvantages because the two functions of impedance transformation and field reorientation have been intermingled. These prior art devices have been difficult to design and fabricate. Thus, these prior art devices have proven unduly costly and have not always effectively provided the broadband reflection-free transmission desired.

Therefore, it is the principal object of this invention to provide an improved microwave transition.

Another object of this invention is to provide an improved microwave transition for coupling a rectangular waveguide to a ridged waveguide.

Another object of this invention is to provide an inn proved microwave transition for coupling a rectangular waveguide to a ridged waveguide, operable over a broad frequency range and Without substantial wave reflection.

Another object of this invention is to provide an irn proved microwave transition for coupling a rectangular waveguide to a ridged waveguide that is more compact, simpler to design, and easier to fabricate than prior art transitions.

The foregoing objects are achieved by providing a microwave transition for coupling a rectangular wave guide to a ridged waveguide wherein the functions of impedance transformation and field reorientation are separated in cooperatinng sections. The transition comprises a hollow waveguide first section of uniform width coupled at one end to the rectangular waveguide and a tapered ridged waveguide second section coupled at one "ice end to the ridged waveguide, the two sections being joined together at their free ends. The height of the first sec tion decreases by steps along the length thereof to trans form from the characteristic impedance of the rectangular waveguide to that of the ridged waveguide. The height of the ridge in the second section continuously increases and the width of the ridge continuously decreases along the length of the second section, so as to maintain the characteristic impedance substantially constant while pro viding for a smooth reorientation of the field configura tion from that in the first section to that in the ridged waveguide. The design of such a transition to provide broadband operation without substantial reflection is sim plified by the separated regions of impedance transfor mation and field reorientation. Furthermore, the transi* tion is compact, simple to design, and easy to fabricate.

The invention will be described with reference to the following drawings, wherein:

FIGURE 1 is a top View, partly in cross-section, of the transition of this invention;'

FIGURE 2 is a front elevational view, partly in crosssection of the transition of FIG. 1;

FIGURE 3 is an exploded view of the transition of FIGS. 1 and 2; and

FIGURES 4A-4G are cross-sectional views of the transition of FIGS. 1 and 2.

The transition iii of the figures is illustrated as providing for the transmission of microwaves in both directions between a rectangular waveguide, denoted generally by the reference numeral 11, and a ridged waveguide denoted generally by the reference numeral 112. Transition It) comprises a first section 14 and a second section 15. Gne end of first section 14 is joined to rectangular waveguide 11 and one end of second section 15 is joined to ridged waveguide 12. The other ends of sections 14 and 15 are joined together. In the figures, waveguides 11 and 12; and sections 14 and 15 are shown formed as a unitary structure; however, it is within the scope of the instant invention to provide that such waveguides and sections are separable and adapted for joining together by conventional techniques, such as by the employment of mating flanges on the coupling ends.

It is the function of first section 14 to provide a progression of characteristic impedance changes therein, such that the characteristic impedance of the section at one end thereof is equal to the characteristic impedance of waveguide 11 and at the other end thereof is equal to the characteristic impedance of waveguide 12. These changes in characteristic impedance are designed to pro vide for the transmission therethrough of microwaves over a broadband of frequencies without substantial reflection. It is the function of second section 15 to provide for the smooth transformation, or reorientation, of the field configuration from that present in section 14 to that present in ridged waveguide 12. Accordingly, sec tion 15 provides a smooth variation in cross-sectional geometry from one end to the other end thereof, the characteristic impedance and cut-off wave length remaining substantially constant as the field configuration is altered from that of a rectangular waveguide of low height to that of the ridged waveguide 12.

The illustrated embodiment of transition 10 is formed of a base member 17 and a capmember 18. Base member 17 is provided with a base plate 20 on which are formed or to which are afiixed upwardly extending steps and ridges to be described hereinafter. Cap member 18 fits over the upwardly extending steps and ridges of base member 17 and the bottom surface of cap member 18 is brazed or otherwise affixed to the opposing portions of the upper surface of base plate 26. Thus,

ber 18 defines a portion of rectangular waveguide 11 at one endthereof, a portion of ridged waveguide 12 at the other end thereof, and first section 14 and second section 15 between such end portions.

First section 14 comprises a plurality of conductive steps, such as steps 22, 23, 24, 25, and 26, disposed within a rectangular waveguide portion comprising base plate 20, top wall 28 and side walls 29 and 30. Section 14 provides a transformation for matching the relatively low characteristic impedance of ridged waveguide 12 and second section 15 to the relatively high characteristic impedance of rectangular waveguide 11. The height of step 26 is adjusted to provide the rectangular waveguide portion defined by the upper surface of step 26, top wall 28, and side walls 29 and 30 with a characteristic impedance equal to that of ridged waveguide 12. The number of steps employed in section 14 is determined by the impedance transformation required, the desired bandwidth of transmission, and the maximum amount of reflected microwave energy which can be tolerated from section 14. Details of the design of a particular first section 14 will be described hereinafter. Each of steps 22-26 extends across the entire interior width of section 14.

Second section 15 comprises a tapered ridge partially sandwiched between a pair of shoulders 36 and 37. Ridge 35 and shoulders 35 and 37 are disposed within a tapered waveguide portion defined by base plate 20, top wall 28, and inwardly tapering side walls 39 and 40 of cap member 18. One end of ridge 35 is affixed to, or joins, one end of step 26. The other end of ridge 35 connects to, or joins, ridge 42 of ridged waveguide 12. The height of ridge 35, at its junction with step 26 is the same as the height of step 26. Ridged waveguide 12 comprises base plate 20, ridge 42, top wall 28, and side walls 43 and 44 of cap member 18. The height of ridge 35, at its junction with ridge 42 is equal to the height of ridge 42. Therefore the height of ridge 35 continuously increases in a direction along the length of section 15 from its value where it joins step 26 to its value where it joins ridge 42.

The height of shoulders 36 and 37 continuously decrease along the length of section 15, from a height equal to that of step 26, where they abut. The shoulders terminate with no height at the entrance to ridged wageguide 12. Thus two channels are formed on each side of ridge 35. One channel is defined and bounded by one side of ridge 35, the upper surface of shoulder 36 and side wall 39. The other channel is defined and bounded by the other side of ridge 35, the upper surface of shoulder 37 and side wall 40. Each of these channels continuously increases in depth along the length of section 15 because of both the decrease in height of shoulders 36 and 37 and the increase in height of ridge 35. These two channels comprise the two stems of a tapered ridged waveguide. The region between the upper surface of ridge 35 and top wall 28 defines the upper cross portion of the tapered ridged waveguide. Therefore ridge 35, shoulders 36 and 37, side walls 39 and 40 and top wall 28 define a ridged waveguide along the length of second section 15, the height of such ridged waveguide continuously increasing and the width of such ridged waveguide continuously decreasing along the length of section 15 from step 26 to ridge 42. At the entrance to ridged waveguide 12 the internal dimensions of the tapered ridged waveguide are equal to those of ridged waveguide 12, so that at this point the width of ridge 35 is equal to the width of ridge 42 and the distance between side walls 39 and 40 is equal to the distance between side walls 43 and 44.

Thus, section 15 provides a tapered ridged wavegniide for transforming, or reorienting, the electromagnetic field from the configuration existing in section 14 immediately above step 25 to the configuration existing in ridged waveguide 12. Thus section 15 transforms the field configuration from the relatively simple pattern in section 14, wherein all electric field vectors are directed vertically and all magnetic field vectors are directed horizontally, into the complex pattern required to satisfy the boundary conditions of ridged waveguide 12. This transformation is effected over a broadband of frequencies without substantial losses or reflection by tapering the ridged waveguide in section 15 such that the characteristic impedance thereof remains substantially constant and equal to that of ridged waveguide 12 and such that the cut-off wavelength remains substantially constant. Details of the design of a particular second section 15 will be described hereinafter.

Thus has been described a novel and improved transition for coupling a rectangular waveguide to a ridged waveguide wherein microwave energy is transmitted between the two waveguides over a broad frequency range without substantial reflection. The transition described is also more compact, simpler to design, and easier to fabricate than prior art devices for accomplishing the same function.

The design of a particular transition will now be described. This transition is intended to couple a rectangular waveguide having an internal width of .900" and an internal height of .400" to a ridged waveguide having an internal width of .202 and an internal height of .400". The ridged waveguide has a single ridge affixed to the lower wall, the ridge having a height of .370" and a width of .030". The transition is designed to transmit, without substantial attenuation or reflection, microwaves in the frequency range of 7.8 to 10.3 kilomegacycles (lame). To minimize the wave reflection, four intermediate steps 22- 25 are employed in section 14. Fewer steps may be used, although the degree of reflection increases as the number of steps decreases. The theoretical characteristic impedance of the rectangular waveguide 11 is computed to be 339 ohms for infinite frequency. The corresponding characteristic impedance for the ridged waveguide 12 is computed to be 98 ohms. The height of step 26 is designed to provide the same characteristic impedance as that of the ridged waveguide; the height of a rectangular waveguide for an infinite frequency characteristic impedance of 98 ohms is computed to be .116". Therefore the height of step 26 is .284". Accordingly, first section 14 is designed to provide an impedance transformation ratio of 339298, or 3.47. Finally, to provide a factor of safety a bandwidth of 0.80 is employed in the design.

Once the specifications have been decided, the step heights may be computed, such as by employing the design tables of L. Young, Tables for Cascaded Homogeneous Quarter-Wave Transformers, IRE Transactions on Microwave Theory and Techniques, pages 233 to 237, April 1959, and pages 243, 244, March 1960. Thus, for a fourstep transformer to provide a transformation ratio of 3.47 over an 0.80 bandwidth the design tables of the Young article specify the following step heights.

Step number: Inches 22 .045 23 .138 24 .224 25 .270

From the Young article a design length for each step is suggested as one-quarter guide wavelength; this length being defined in the article. A first section 14, constructed according to the above design provides the requisite impedance match over the design frequency range with a minimum of reflected waves.

Second section 15 is adapted to provide for the transformation of the microwave field. The height of ridge 35 at the end adjacent step 26 is equal to the height of step 26. The height of ridge 35 adjacent ridge 42 is the same as that of ridge 42. The height of ridge 35 between step 26 and ridge 42 has a constant slope, so that the upper surface of ridge 35, as seen in FIG. 2, represents a straight line connecting the tops of step 26 and ridge 42. The width of ridge 35 is determined by the widths of shoulders 36 and 37. The width of each of these shoulders is constant and equal to the distance between a side of ridge 42 and the opposing one of side Walls 43 and 44. The height of shoulders 36 and 37 at the ends adjacent step 2.6 is equal to the height of step 26. At their other ends the height of these shoulders diminishes to zero. Thus, in "FIG. 2, the upper surface of shoulder 37 represents a straight line connecting the top of step 26 and base plate 26). The length of second section should be at least one guide Wavelength, wherein the guide wavelength is the wavelength of the microwaves in traveling along section 15. By maintaining a substantially linear increase in height and decrease in width of ridge 35 between step 26 and ridged waveguide 12, the characteristic impedance and cut-off Wavelength remain substantially constant along the length of second section 15. The constant character istic impedance of section 15 is equal to that of ridged waveguide 12. The cut-ofi" wavelength of section 15 is equal to that of both rectangular waveguide 11 and ridged waveguide 12. The cut-oft wavelength in the tapered ridged waveguide is proportional to the mean distance from the upper surface of shoulder 36 over the top of ridge 35 to the upper surface of shoulder 37.

Accordingly, the unitary combination of first section 14 and second section 15 is a simply designed and easily fabricated transition between rectangular and ridged waveguide, providing for the transfer of microwaves there through over a broad frequency range Without substantial attenuation or reflection.

While the principles of the invention have been made clear in the illustrative embodiments, there will be obvious to those skilled in the art, many modifications in structure, arrangement, proportions, the elements, materials, and components, used in the practice of the invention, and otherwise, which are adapted for specific environments and operating requirements, without departing from hese principles. The appended claims are therefore intended to cover and embrace any such modifications within the limits only of the true spirit and scope of the invention.

What is claimed is:

1. A transition for coupling a rectangular Waveguide to a ridged waveguide comprising first and second sections joined together; said first section comprising a hollow rectangular waveguide portion and a plurality of conductive steps disposed within and along the length of said portion, each of said steps extending between a set of opposite walls of said portion, the height of each of said steps being greater than the heights of the preceding step in a direction along the length of said first section from one end to the other end thereof, the height of the step closest to said other end of said first section providing a characteristic impedance for said other end substantially equal to the characteristic impedance of said ridged waveguide, the internal cross-section of said first section at said one end thereof being the same as the internal cross-section of said rectangular Waveguide; said second section comprising a hollow outer member and a ridged member disposed within said outer member, said outer member continuously decreasing in internal width and continuously increasing in internal height in a direction along the length of said second section from one end to the other end thereof, said ridge member continuously decreasing in width and continuously increasing in height in said direction along the length of said second section, the internal cross-section of said second section at said other end thereof being the same as the internal cross-section of said ridged waveguide; and said one end of said second section being joined to said other end of said first section.

2. The transition of claim 1 wherein the width of said first section is uniform.

3. The transition of claim 2 wherein the internal widths of said one end of said second section and said other end of said first section are equal.

4. The transition of claim 3 wherein the internal heights of said one end of said second section and said other end of said first section are equal.

5. The transition of claim 4 wherein the cut-off Wavelengths of said rectangular waveguide and said ridged waveguide are substantially equal.

6. The transition of claim 5 wherein all cross-sections of said second section have the same theoretical cut-olf wavelengths.

7. A transition for coupling a rectangular waveguide to a ridged waveguide comprising first and second sections coupled together; said first section comprising a hollow rectangular waveguide portion, the height of said portion progressively decreasing in a direction along the length of said first section from one end to the other end thereof, the internal cross section of said first section at said one end thereof being the same as the internal cross section of said rectangular waveguide; said second section compris ing a hollow outer member and a ridged member disposed within said outer member, said outer member decreasing in internal Width and increasing in internal height in a direction along the length of said second section from one end to the other end thereof, said ridged member decreas ing in width and increasing in height in said direction along the length of said second section, the internal cross section of said second section at said other end thereof being the same as the internal cross section of said ridged waveguide; and said one end of said second section being joined'to said other end of said first section.

References Cited by the Examiner UNITED STATES PATENTS 2,767,380 10/56 Zobel 333-35 2,802,991 8/57 Coale 33334 3,019,399 1/62 Lanciani et al 33398 HERMAN KARL SAALBACH, Primary Examiner. 

7. A TRANSITION FOR COUPLING A RECTANGULAR WAVEGUIDE TO A RIDGED WAVEGUIDE COMPRISING FIRST AND SECOND SECTIONS COUPLED TOGETHER; SAID FIRST SECTION COMPRISING A HOLLOW RECTANGULAR WAVEGUIDE PORTION, THE HEIGHT OF SAID PORTION PROGRESSIVELY DECREASING IN A DIRECTION ALONG THE LENGTH OF SAID FIRST SECTION FROM ONE END TO THE OTHER END THEREOF, THE INTERNAL CROSS SECTION OF SAID FIRST SECTION AT SAID ONE END THEREOF BEING THE SAME AS THE INTERNAL CROSS SECTION OF SAID RECTANGULAR WAVEGUIDE; SAID SECOND SECTION COMPRISING A HOLLOW OUTER MEMBER AND A RIDGED MEMBER DISPOSED WITHIN SAID OUTER MEMBER, SAID OUTER MEMBER DECREASING IN INTERNAL WIDTH AND INCREASING IN INTERNAL HEIGHT IN A DIRECTION ALONG THE LENGTH OF SAID SECOND SECTION FROM ONE END TO THE OTHER END THEREOF, SAID RIDGED MEMBER DECREASING IN WIDTH AND INCREASING IN HEIGHT IN SAID DIRECTION ALONG THE LENGTH OF SAID SECOND SECTION, THE INTERNAL CROSS SECTION OF SAID SECOND SECTION AT SAID OTHER END THEREOF BEING THE SAME AS THE INTERNAL CROSS SECTION OF SAID RIDGED WAVEGUIDE; AND SAID ONE END OF SAID SECOND SECTION BEING JOINED TO SAID OTHER END OF SAID FIRST SECTION. 